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Direct Measurement of Evapotranspiration (ET)
Who (or what) is this eddy you keep talking about?
Efficient water management has never been more critical for agriculture and specifically for viticulture. High-end viticulture needs to manage water to not only cut costs, but to keep quality high in a market of oversupply and buyers who hold the upper hand over the grower. High production viticulture may not need the water management finesse for quality that high-end viticulture does, but regulatory demands for groundwater protection as well as limitations on water deliveries push growers into making the most out of every gallon.
Here at AV, we’ve made use of impactful technologies to help growers irrigate efficiently and control vine stress to improve wine quality from their vineyards. Our primary tools have been the soil moisture probe and, more recently, the Florapulse microtensiometer. Both tools have been indispensable and even more so now that we have our own data portal to view and analyze these data streams. More recently, we’ve been working with a new tool, an eddy covariance device, for direct measurement of ET, which gives us another approach for irrigation management that we didn’t have before. Before I introduce this new tool, let me explain what direct measurement of ET is and how it differs from other ET measurements.
Eddy Covariance – who is this guy?
Eddy is not just your buddy down the road with whom you share a good laugh occasionally. Eddy or more meaningful, eddies, are swirls of turbulent air which we experience daily but don’t give a lot of thought. Unless you’re a micro-meteorologist like I am. Yes, I am one of those. I did my Ph.D. in micrometeorology of the vineyard environment so I know a thing or two about it. Let me give you the nickel tour of micrometeorology (let’s call it micromet for short), eddies, and how eddy covariance is used to measure ET.
Wind does not blow in a straight line. As air flows across the earth’s surface, or on a micromet-scale, the surface of a field, forest, desert, or whatever, it experiences friction from that surface. Air flow at the very surface of the earth is zero, because wind cannot penetrate the earth. So, as the wind blows across the surface, the portion closer to the ground experiences drag from the friction, which is enhanced by objects, such as buildings, trees, and of course grapevines. This friction causes a shear force in the air flow field, which creates the turbulent eddies. And these eddies swirl and interact with other masses of air, creating more eddies. These wind shear eddies are smaller than the primary eddies, and these smaller eddies interact with other packets of air, creating their own eddies. And so on and so on. So, indeed air does not flow in a straight line, with some exceptions like katabatic wind during the very still night when cold air sinks. Those flows are not turbulent, but during the day, you can count on turbulent eddies all over the place. You can see this if you look at smoke rising and then swirling: initially it rises quickly because of convection from the heat, but as it cools, it gets taken by the air and you can then see what the eddies look like.
So, now that you know what an eddy is, let’s discuss why It’s important to us, not only for agriculture, but as humans. Without air movement, everything that is generated at the earth’s surface (e.g. dust, CO2, farts, and yes water vapor) would have to rely on diffusion from high concentrations at the surface to lower concentrations in the atmosphere above. Thankfully, that is not the case. The wind, with its turbulent eddies, facilitates the movement of gases and suspended particles (called aerosols) from the surface to the sky.
In the case of water vapor, the water vapor concentration (when it is not raining) is higher within and just above a plant canopy than it is in the air above the canopy. Turbulent eddies mix the moister air below with the drier air above (Fig. 1). In the portion that is swirling upward, vapor is brought upward. In the portion that is swirling downward, drier air is brought downward.
We can measure this! Eddies can be measured using high-speed anemometers. A sonic anemometer looks like a stethoscope, but it is really a pair of speakers and microphones. Several times per second the speakers emit an ultrasonic pulse, which is captured by the microphone on the other end. The time it takes for the sound wave to reach the microphone on the other end is measured and the difference in time between the two directions is a measurement of instantaneous wind speed. We can measure the turbulent air field this way and meteorologists can measure this in 3-D. For us, we only care about one axis – the vertical one. Because movement horizontally just moves vapor across the field and we only care about what is moved upward. So, the 1-dimensional sonic anemometer measures the fluctuations in vertical air movement. Over time, the net air movement is zero because the earth blocks vertical air movement. So, we only care about the fluctuations in the vertical direction.
We can also measure water vapor, or humidity, at the same high frequency. When air swirls upward, the moisture air registers an increase in humidity and when it swirls downward the drier air brought in registers a decrease in humidity. If we record the instantaneous vertical air velocity along with the instantaneous humidity, and take the covariance of the two over a time interval, we get a direct reading of water vapor flux. This is what eddy covariance is!
If it sounds complicated, you’re right it kind of is, but fortunately this is established technology and the covariance is computed on the fly by either the device itself or the equipment used to log the data. In my graduate research, and in my early professional career, I used eddy covariance equipment. The cost back then was about $30,000 in today’s dollars. You can find them now for that or much higher for use in micromet research. So, while eddy covariance equipment has long been the gold standard for ET measurements, its high cost has rendered it primarily a research tool, though developers of other ET methods have and are still using it as a standard to calibrate their approach.
That’s nice, but the gold standard is too expensive to use to directly measure ET
That’s right, equipment for eddy covariance has been just too costly to use as a source of daily ET measurements. Until recently, at least. Last year Li-COR, a company out of Nebraska who have been making plant and environmental research equipment for decades, released their LI-710 Evapotranspiration Sensor (Fig. 2), which is a simplified, but still effective, eddy covariance sensor in a small and rugged package. The best thing about it is the price tag, which is a fraction of the cost of a traditional eddy covariance system and puts it right into the cost-effective range for commercial agriculture. The device computes eddy covariance internally and communicates digitally to a datalogger.
Last year, overjoyed with this new technology, we entered into a reseller agreement with Li-COR and purchased some units to get more familiar with and to do some design for the best data logging and telemetry solutions. We’ve made substantial progress and have also developed an app to track ET and to help growers make determinations of irrigation from the information (Fig. 3).
Why use this over other ET measurement methods?
Our motivation for this blog post is to announce this new technology and not to disparage other technologies out there, but we should at least briefly discuss why it is such an exciting development for us and for agriculture in general.
Probably the most common way to obtain ET measurements is by using weather stations and using that information to determine reference ET (ETo) using the modified Penman equation. Weather inputs of solar radiation, wind speed, temperature and humidity are used to determine Daily ETo. Almost all weather stations will provide values for ETo, as this is a standard and common method. That said, ETo itself has limited utility, as it is based on the theoretical ET of a hypothetical reference crop (a mixed grass mowed to a certain height) and does not indicate the ET of the crop (ETc). For many crops, including grape vineyards, ETc is a fraction of ETo.
To determine ETc, ETo is multiplied by a crop coefficient (Kc). These crop coefficients are basically a “fudge factor” to represent the fraction of ETo that the actual crop experiences. Kc values will vary during the growing season as the canopy develops and then senesces, usually peaking around veraison, holding steady and then dropping near or after harvest. Kc values have been computed and published by many researchers for many different crops, including grape vineyards. However, they are prone to error and we have found, using soil moisture as our guide, that we can irrigate far less than the amount ETo*Kc produced without long-term loss of soil moisture. So, actual Kc is likely substantially lower than published values of Kc are telling us based on our experience.
In fact, last year we ran some REAL ET eddy covariance measurements and compared them with ETo computed from nearby weather stations and found effective Kc values of around 0.35 for a full canopy in three vineyards, compared with published values of around 0.6. That’s a big difference!
Surface renewal has been a popular method of ET determination in recent years. While surface renewal is a valid micromet method, we should caution that it is not a direct ET measurement. Rather, it is based on a surface energy budget (Fig. 4). Let me explain. The energy budget of a field (or any other part of the Earth’s surface) is comprised of four basic flux components:
1) Net radiation flux, Rn, which is the amount of solar radiation that provides energy to the surface (downwelling radiation minus reflected radiation)
2) Ground heat flux, G, which is energy that warms the surface of the soil and penetrates into deeper levels
3) Sensible heat flux, H, which is energy dissipated into the air by heating of the air from soil and leaves and is transported into the ambient environment by turbulence, just like water vapor is
4) Latent heat of evaporation flux, LE, which is energy used to evaporate water from liquid into vapor, which is then transported into the ambient environment by turbulence, just like sensible heat is.
The surface renewal approach measures not latent heat flux or water vapor flux, but it measures sensible heat flux. To determine latent heat flux, and from that, evaporation flux, the energy budget is used to net out that term. Usually, the other two terms, Rn and G, are estimated, and whether or not estimated or measured, each term in the energy budget equation represents a source of potential error. The net of it is that surface renewal is prone to error, unlike eddy covariance, which is a direct measurement of water vapor movement and does not require any assumptions or models.
Are there any limitations on where eddy covariance can be used?
Yes, there are limitations, which are pretty much the same limitations that surface renewal has. The field needs to be a decent size – large enough to provide a few hundred feet of upwind fetch to the sensor. This is to allow the flow field to stabilize and avoid edge effects, like from roads and ponds. And while the field should ideally be flat, sloped fields can be used as long as the slope is relatively consistent. We tested the LI-710 over some uneven and sloped vineyards last year and got good readings from those, but site selection is important and tiny little “island” vineyards are simply not candidates. This is true for both surface renewal and eddy covariance sensing techniques.
That said, most commercial-scale vineyards will be able to use this new device and we look forward to rolling them out to early adopters in this and upcoming growing seasons!
An Honest Look at No-Till
It's not for the faint of heart
Going no-till certainly has been picking up steam in recent years, and overall it’s a good thing. When I first got involved in viticulture back in 2010 I was living in Italy. Like a lot of Mediterranean viticultural areas, there was a tendency to disc everything all the time. If you didn’t have a barren wasteland with vines poking out of it, you weren’t a good farmer. Anything you couldn’t get to with a tractor you sprayed with herbicide. One of my first vineyard jobs in Italy was spraying glyphosate out of a backpack sprayer all spring. I felt like I was in the final scene of the Godfather! Minus the dying part.
Herbicide: the new four-letter word
Mentalities have shifted since then both in Europe and here in the states. All in all it’s a good shift. We’ve all seen places that have gone on for years and years using herbicide to a point where you don’t even need to spray it anymore because that soil is so dead. The only thing that grows on it is that weird reddish moss.
Percolation suffers. The soil forms a crust on top and water can’t infiltrate it. You’ll walk these vineyards and you see the water from the emitter just beads up and drips off the berm like Teflon. Then it pools in the tractor row. There is just no porosity to these soils and it makes irrigation almost impossible.
Aside from that, herbicides are gross. We’re lucky in vineyards to not use too many nasty chemicals but the ones that are nasty are all herbicides especially the pre-emergent ones.
Herbicides also have developed a bad rap among consumers especially roundup or glyphosate, which is ironic because it really isn’t that toxic compared to others. As an aside, there are a bunch of people out there who seem to think that glyphosate is the same thing as Agent Orange. For the record that is very not true. They are completely different chemicals. Commercial forms of glyphosate can be orangey in color. The resemblance ends there.
The trouble with tilling
Conventional tillage can also be problematic. Frequent tilling destroys soil structure. If you break a chunk of undisturbed soil apart, you’ll find that it breaks into aggregates of soil particles. Inside those aggregates you’ll find different sized pores, both big ones that hold air and tiny ones that hold water. Plants need both of these things to thrive. The aim of tillage is to break these aggregates up into smaller bits but long term that is going to negatively affect your plants.
Tillage also leads to compaction, again over time. Then the only way to break it up is with more tillage. It’s like one of those vicious things!
No-till coupled with covercropping helps build soil structure improving water-holding capacity and aeration of the soil by way of better porosity. It does this at the same time as it builds organic matter. Organic matter is a source of nutrients for the vines. Everything contained in the plant decomposes and becomes available to the vine. This is particularly important in the case of leguminous covercrops that fix nitrogen. Organic matter has a negative surface charge and so it holds onto all the positively charged cations your vine needs namely Ca, Mg, and K.
The breakdown of old plant matter into organic matter is driven by microbes and this is what people mean when they talk about the “living soil”. Herbicides and tillage disrupt the lifecycles of soil microbes and limit their ability to do this. No-till is supposed to leave these little guys alone to do the work we need to free up nutrients and make them plant available. In theory anyway.
Mismeasure of microbes
I say in theory because this is really hard to measure. I think this is one of those areas where agriculture lapses into the religious. Basically, it’s a hard thing to sample for and we see this all the time sampling for nematodes. You may have one pocket over here that has this number of some kind of microorganism and a few feet over you have a different one. It’s hard to establish scientifically that one tillage treatment or another favors diversity of microorganisms or how numerous they are. Many of the papers out there come up inconclusive even if it makes total sense that if you mess with something’s environment they aren’t going to thrive as much as if you left it alone.
But there are some shining examples of work that support this idea. Chen et al. found that conservation tilling (i.e. no till and reduced till) increased total soil microbial biomass by 37% at least in the top 8” of the soil. They found that this only worked in loamy soils, and that sandier or coarser textured soils didn’t see the same effect. This is mostly because you need higher levels of soil carbon and sandy soils don’t have a whole lot of that. It showed what we expected that fewer disturbances allowed for more efficient use of that soil carbon. Basically, the microbes did a better job breaking things down if you didn’t run a plow through their house every couple of months.
Nunes et al. is another paper that explored this topic. They looked at seven different indicators for soil health:
- Soil organic content
- Microbial biomass carbon, which is a measurement of carbon contained in the living portion of the soil i.e. microbe bodies
- Nitrogen
- Soil respiration, which is proxy for microbial activity
- Active carbon, which is the carbon that is available to the microbes
- Beta glucosidase, which is the enzyme involved in the degradation of cellulose (plant bodies)
- Soil protein, which is the soil’s ability to store nitrogen
They found that every one of these measures was improved by reducing till. Again, this is usually something we see only in the top portion of the soil (top 8”).
The bigger picture
Now neither of these studies are on vines. If you’re looking for some reading material on no-till in vineyards, Richard Smart from UC Davis did some incredible ahead of his time work. I urge you to take a look at some of his papers. This one in particular puts no-till into the context of global warming, which if anything, is the real reason we all should be looking at moving in this direction.
Bottom line is that untilled land sequesters more carbon than tilled. ½ of all the carbon in the atmosphere is estimated to come microbial respiration of carbon on the surface of the soil. A lot of this comes from the large-scale repurposing of land that has occurred over the last 200 years. All nitrogen (nitrous oxide is also a greenhouse gas) comes from microbial activity on the surface of the soil.
Covercrops alone don’t help the problem. Yes, the covercrop sequesters a lot of carbon but if you then till that into the soil, the benefit is lost. All that carbon gets released and it gets released quickly.
This is a great study. They looked at one vineyard over seven seasons and found that going no-till sequestered 1.5 metric tons per acre. It also increased the oxidation of methane which is good even though that technically increases CO2. Methane’s global warming potential is 27 times that of CO2 so less methane is a good thing.
This study also took into account fuel burned up during tractor passes as well as N20 production. No-till is net negative. Even going to occasional tilling tipped the scales not just because it released sequestered carbon, but also just because it meant another tractor pass.
The limitations are numerous
From a practical standpoint, what does it mean to go no-till? The first limitation we face is that, you have another plant whether a covercrop or a weed, that competes with your vine for water and nutrients. This is going to be a lot more severe if you are going wall to wall no till i.e. where you leave the undervine row untilled as well. Most growers we work with if they do go no-till opt for just leaving the midrow or the tractor row untilled. Leaving the undervine untilled is a whole lot harder.
A lot of the studies that are out there on no till point out that going no-till significantly reduced yield in whatever crop they were working on. Grapes are a little different since, if you’re a fine wine maker, yield may not be your main target. Some of the growers I’ve spoken to about their experiences say that in the first year they noticed stunted growth. Keep in mind that the cover crop is growing in the spring, right when your shoots are trying to develop. It’s the worst timing, but there’s not a lot you can do about it. This is of particular importance in climates with wetter winters. In those cases, there’s a lot of spring nutrient uptake that goes on in the midrow since roots are active there due to all the rainfall. Other dryer areas go into the growing season with pretty dry soils so the only area where you have to worry about competition is right under the emitters.
There seem to be a lot of growing pains in the first year of switching to no-till as you’re suddenly without the easy button to deliver a slug of nutrients to your vines. The benefits that no-till provides are soil structure and organic matter. These things take some time to form. You may need to fertilize more than you normally do. If you’re an organic producer, which you may be if you’re considering no-till, that’s going to be a significant expense if you suddenly have to give everything a shot of expensive organic nitrogen.
On the flipside, if you have an overly vigorous vineyard, no-till can do a good job soaking up some of that extra vigor.
Plants don’t just compete they actively sabotage by way of what’s called “allelopathy”. If you’ve ever wondered why your vines look like crap around an oak tree, that’s allelopathy. Vines don’t play well with others and some weeds and covercrops especially if they’re in the vine row have a similar action.
Another limitation is that there is no ideal covercrop. Ideally you have a nice low-lying covercrop that you can seed once. It reseeds itself. It doesn’t take over. It gets tall and you cut it and it shades out all other growth. In the case of grasses, you have to cut before they seed otherwise they’ll be too tall. Leguminous cover crops aren’t nearly as assertive, but they also don’t provide nearly as much organic matter or ground cover.
The big problem that a lot of growers face when going no-till is rodents. That nice mulch you create by mowing is the perfect place for gophers and ground squirrels to hide. If you have untilled vine rows, voles can be a problem. I’ve seen new vineyards (and some fairly mature ones) scrapped entirely because voles girdled the trunk of every vine.
Tilling also does a really good job of getting rid of burrow systems, which is important if you struggle with ground squirrels and gophers. The occasional till chops those guys up and doesn’t allow them to build a city under your vineyard. I’ve seen infestations of ground squirrels so bad you can’t even take a step without falling through the ground into a burrow. They will eat the roots right out from under your vine.
Definitely not the easy-button
All of this boils down to the fact that going no-till is going to be more expensive and more time-consuming than conventional farming. The growers I’ve spoken to who have gone no-till have a worker whose specific job is trapping rodents for at least two to three days a week all season long. That adds up to a lot.
Another thing to consider when going no-till is that you’ll probably need some specialized equipment. If you’re just doing the tractor row no-till, a mower may suffice plus a weed knife…assuming you are also getting rid of herbicide. There are a lot of fun toys out there that you can check out for undervine weed control. The finger weeder is an interesting one. It’s actually a passive implement that doesn’t require any power from the tractor to work. It just rotates with the forward movement of the tractor. The Multiclean is another minimal-disturbance implement. Our farming company has one of these and they seem to like it. Timing is really everything. If you let the brush get too high, you will have a tangled mess on your hands. It’s especially hard in vineyards with high-water holding capacity as you may not be able to enter the vineyard with a tractor before the weeds have already taken over.
You’ll need to rethink how you reseed your cover crop. You can’t just broadcast seed over an untilled surface and assume they’re going to take root. There are some direct seeders out there specifically for this reality but again, it’s an investment.
The limitations to undervine weeding or tilling, if you’re still planning on tilling the vinerow are topography and vine spacing. These implements are always harder to use on a steep and/or uneven incline. If you have tight vine spacing, the tool may not have time to fully rebound and swing back in between vines. That will leave a lot of missed spots.
One thing to keep in mind when transitioning to a reduced or no-till system is to adjust your expectations. Nothing looks cleaner than an herbicided vineyard. You’re going to have missed spots here and there and you’re going to have some weeds. Getting over the mental block is a big one for some people.
Find what works for you
Even if you aren’t going hard core no-till, there are ways to simply reduce tillage, which is still a step in the right direction. A lot of vineyards we work with till alternate rows and switch every 3 to 5 years. As I mentioned, wall to wall no-till under the vines is a whole lot harder, so maybe you just want to keep your midrow non-tilled and use a weed knife undervine. That’s still good.
If this is something you want to do, the best option is to design future blocks with no-till in mind. The above picture is from a ranch in Paicines managed by Kelly Mulville, who’s the viticulturist who thought this design up. He’s trained the vines on a high wire and the dripline is also really high. This allows him to run sheep all year long, which is great because normally you have kick your sheep out once your vines get tasty. The high dripline too is a really good idea. It makes a lot of undervine implements easier to use as a low dripline gets in the way. I know growers who have spent all winter raising the dripline wire 6 inches just so they can get a Multiclean to work.
There are some places where despite the benefits, we really don’t recommend no-till. Don’t plant a new vineyard on untilled soil. Your baby vines are not going to be able to handle the competition. Also ripping is the only way to break up any hardpans you have and incorporate any amendments that you’ve added.
Rodents can get out of hand and so can weeds. If you have an outbreak of star thistle or something else that is really aggressive or if you have an underground city of squirrels under your vines, just till. There’s no point in being a martyr.
The picture above is of a vineyard on Mount Etna in Sicily. The Etnean viticultural area is spectacular and it’s almost completely tilled, mostly because they have this one kind of wild chestnut that, if left alone for a season, will grow a tree right in the middle of your vineyard. Like Etna, there are some places where no-till just doesn’t work.
If this is something that interests you though. Go for it. Throw everything against the wall and see what sticks. Like everything, a one-size-fits-all mindset isn’t going to work. If you’ve been growing grapes for a while though, you already knew that.
Articles:
Chen, H., Dai, Z., Veach, A. M., Zheng, J., Xu, J., & Schadt, C. W. (2020). Global meta-analyses show that conservation tillage practices promote soil fungal and bacterial biomass. Agriculture, Ecosystems & Environment, 293, 106841.
Nunes, M. R., Karlen, D. L., Veum, K. S., Moorman, T. B., & Cambardella, C. A. (2020). Biological soil health indicators respond to tillage intensity: A US meta-analysis. Geoderma, 369, 114335.
Wolff, M. W., Alsina, M. M., Stockert, C. M., Khalsa, S. D. S., & Smart, D. R. (2018). Minimum tillage of a cover crop lowers net GWP and sequesters soil carbon in a California vineyard. Soil and Tillage Research, 175, 244-254.
Planning on Automating Irrigation This Year?
Read this first!
As agricultural consultants in California, irrigation consulting during the growing season is our bread and butter. A lot of times, especially in vineyards with lighter soils where I recommend short and frequent irrigations, I know my desired schedule amounts to a tall order. Not everyone can feasibly do two hours, three times a week. No matter what’s best for the vines, I have to work with a human irrigator, who is still going to turn the valve on at 5 pm and turn it off at 7 am the next day.
In a lot of cases, this amounts to a vineyard that is both over- and under-watered: the 14-hour irrigation percolated past the rootzone in under 3 hours and the rest of the week (after the root zone water was depleted) the soil was dry as a bone.
So, I’m happy to see so much interest these days in valve automation.
I’m also apprehensive because I’ve automated valves and it’s not a silver bullet. It’s not any bullet. It’s a useful tool that needs to be applied to what is already a functioning irrigation system. And some of y’all don’t have that.
How does valve automation work?
To get why this is the case, you have to understand how automatic valves are automated. You may have a diaphragm or a bonnet valve in the vineyard already that you manually turn on and off. That valve is then automated via a solenoid, which is a small electromagnetic device with a plunger. When actuated, the plunger moves up to open the valve, or down to close it.
Given that very few farms have line power at valve locations to provide the constant AC power needed to hold open the solenoids, most ag valves use solenoids known as “DC latching solenoids”. They are actuated by ~12V pulses of electric current powered by a solar panel/battery, and held in that position by a mechanical latch. This can be reversed by applying a reverse polarity pulse, in which case the plunger is latched in the opposite state. These actions are triggered by the control system which is ultimately controlled by you via whatever app came with the automating system.
The contact between the solenoid plunger and the actual closing mechanism can be either direct, indirect, or semi-direct (see above video). Most situations you see in vineyards are indirect. The solenoid plunger basically just redirects water from moving on one side of the diaphragm to the other. This creates a pressure differential to open the valve or a pressure equalization to close the valve. The water pressure itself is used to both open the valve and to close it.
This is nice because you can open and close a high water flow valve using only a tiny solenoid plunger actuated with very little energy. The water pressure itself is doing all the work. This is why, for example, a 6-inch valve can be operated using the same solenoid as a 2-inch valve.
The million-dollar question: What if you don’t have enough pressure?
Long story short, your valve isn’t going to open or close the way it should.
To get a more complete answer, I got in touch with Saul Medrano over at AvidWater. Saul has a lot of experience with valve automation in everything from greenhouses to berry farms to vineyards. Vineyards tend to have more challenging topography than other growing situations, so I was interested to hear his opinion on some of the common culprits of dropping pressure in these cases. According to Saul:
“Incorrect usage and placement of air vents is a big one. Some people may think that just because there is an air vent, it’s going to work, but really it depends on what air vent you have and where. That and just not understanding what pressure losses you get across all the components like valves, air vents, filters, check valves. You need to understand what it takes for them to work properly.”
He added:
“You really have to stick to whatever the manufacturer says the valve can handle. If the manufacturer says, ‘Hey, this thing can operate properly at 10 PSI’, it should be able to operate at that.”
There are some creative work arounds out there. Anytime water passes through a filter, there's a drop in pressure whether it's clogged or not. You may have high pressure at your pump but low pressure at your valve, especially with changes in elevation.
And you may not even have that…
A few years ago, we installed 10 PSI (threshold) pressure switches wherever we had soil moisture probes we monitored to give us irrigation feedback for our weekly recommendations. This was effectively just to measure the duration of irrigations: switch turns on when irrigation starts and turns off when irrigation stops. We chose 10 PSI assuming that people would have at least that in their driplines. For the record, most pressure-compensating drip emitters are designed to function between 12 and 58 PSI. Below (or sometimes above) that range, the emitter output will be erratic and outside the specified flow.
We found in many blocks both hilly and flat, the irrigations failed to actuate the switch. This means that when irrigations get going, the line isn’t even being pressurized to 10 PSI. Aside from issues with distribution uniformity of water and fertilizer, a system like this would need to be automated specifically with valves that could function at low pressure. We’ve often seen automated valves that don’t work consistently because of low system pressure. This usually translates into a valve that doesn’t shut off once it’s turned on because the pressure is too low to impact the diaphragm.
At the source, the pressure these growers are getting is probably adequate. That doesn’t mean that by the time it gets to the valve the pressure is the same. In fact, laws of physics dictate that it is not the same. Filters, fittings, pipes themselves and changes in elevation continually eat away at the pressure you have in your system and that will determine what your options are for automating.
I asked Saul what some of the reasons for poor pressure in vineyards are. He responded:
“Over the last three years, obviously, it’s been a tough market. There are a lot of designs out there that are just designed to be cheaper. Everyone has sacrificed some performance in the system to reduce cost. If your irrigation system isn’t designed properly and you’re not using the right equipment to handle that, low-pressure or high-pressure system, then it’s not going to work.”
And on the other hand,
“I’ve seen some sites where they have all the bells and whistles. They have a VFD (i.e. Variable Frequency Drive) at their pump. They have a pressure-regulating valve at the irrigation site. And then they have pressure-compensating emitters. The diaphragm valve with the pressure-reducing pilot is going to open and close to try to match the pressure that it needs. And in turn, the pressure-compensating emitters are going to do the same thing. You have three things that are trying to achieve this one common goal, and it just creates chaos.”
Most modern irrigation installations I’ve seen have a VFD either installed in tandem or built into the pump control. In the past, VFDs have been incentivized via several government programs (e.g. EQIP, SWEEP). However, just having a VFD isn’t the end of the story. Saul reiterated:
“There’s a misconception that if you have a VFD, you’re going to have the most energy-efficient pumping system. That’s not always true. It may use less energy, but it’s not necessarily going to be the most efficient usage. All it’s going to do is vary the speed of the motor to ramp up or down based on whatever pressure you’re trying to achieve. You need to make sure your VFD is programmed properly in order to have the most efficient energy use that you can have.”
Don’t let me scare you
Saul and I agree that automation is a good thing. With rising labor costs, it’s becoming more of a necessity. It’s also more time efficient when you have to get water to a bunch of blocks in the course of a week. When asked if he had any advice for those thinking of automating, Saul said:
“I think the first thing anyone should do if they’re interested in automation, is do some remote monitoring. Put some sensors on your field and keep track of what’s going on. You can monitor flow, monitor pressure, monitor EC, pH, just know what’s going on now in your field. Then you go into valve control. Now you have control and monitoring. I think everyone should have good data based off a sensor, not from a person who’s subject to human error.”
Lumo valves contain a flowmeter and pressure switch to both automate irrigations and monitor flow and pressure. This allows the grower to quantify their water use on a block-by-block basis and detect problems in realtime.
The com-bi-nation valve control and flowmeter
Let’s talk about the new kid on the block, shall we?
Lumo seems to be the latest and greatest in irrigation Agtech and they certainly give us a lot of food for thought. For those who aren’t familiar with the product, Lumo offers an all-in-one valve with built-in flowmeter and telemetry for control and monitoring. Compare this to a more classic automation arrangement where the telemetry device is wired to an external solenoid and (hopefully) a pressure switch (or transducer) to determine whether the valve actually opened and closed when you told it to.
Instead of working via a solenoid, Lumo valves work via a worm drive mechanism that moves up or down when actuated and directs the flow of water over or under the diaphragm. I’ve worked with a couple devices that use this method in place of a solenoid and they seem to perform better in low-pressure systems. Regardless, these valves are specified to operate at between 15 and 80 PSI and I would stick to manufacturer’s specifications…always.
Lumo solves an issue we often see in viticulture where individual valves are spread throughout the vineyard. In the past, this arrangement made automation expensive given that each valve needed its own telemetry device, which typically starts at around $1800. If all your valves are located at one central location, you may have automated years ago because one device can service a handful of valves. Single Lumo valves clock in under half of this price tag, so it’s a good option for when you have valves scattered around the farm.
What Lumo hangs its hat on though is its continued monitoring of water usage and fluctuations in flow. This allows for precise applications of water to each block as well as keeping a lookout for leaks and blowouts. For a lot of growers who have used Lumo, there tends to be a big discrepancy between how much they thought their output would be and what it is.
The above photo showcases how Lumo can be used to detect problems in an irrigation system. If the reported GPM is much higher than what you expected, you may have a leak, or in this case, a malfunctioning air vent.
Kick the tires
Will automation work in your vineyard? The best way to determine that is to have a qualified irrigation professional assess your system. Here at Advanced Viticulture, we partner with irrigation specialists throughout California to ensure that you put your best foot forward in any project. As Saul said,
“Automation is not going to fix a poorly designed system. You need to understand how your system works and make sure that it’s designed properly to handle an automation system on it. We’re honest with customers. We’re not going to sell them a system if we know it’s going to fail. We’ll say, hey, you need some upgrades to do before any automation to work here. I would say that’s a really important thing that sounds like common sense, but I’ve seen some stuff out there that had no business being installed.”
For the most part, no automation company, Lumo or otherwise, wants the application of their equipment to fail. Dissatisfied customers are infinitely more vocal than satisfied ones. It’s one of the reasons Lumo works with companies like AvidWater and Advanced Viticulture to make sure their product is a good fit for each system prior to installation. Regardless of what company you go with, ask around. Ask the company selling you the devices to put you in touch with an irrigation expert. Then plan your budget accordingly. You may need to do some work on your infrastructure first and put off automation for a year or two. That’s still better than getting stuck with an expensive system that doesn’t work.
New Water and Weather Information Portal
We have a new water and weather information portal we'd love to show you. We designed the portal ourselves, based on decades of working with other data systems. We can connect to most data telemetry systems out there - probably yours too. We'll be demo-ing the portal at our Unified Wine and Grape Symposium booth 1245.
We are now working with Li-COR's LI-710 evapotranspiration (ET) sensor. This sensor provides a direct measurement of REAL ET, not a derived version of ET that other systems use. This is an eddy covariance based technology that measures actual water vapor flux. We will have the sensor in our booth and would be excited to discuss it with you.
We are now working with Lumo automated valve technology and are excited to add them to our growing list of technology partners.
We continue to deploy Florapulse microtensiometers, which measure plant water stress continuously. These devices have shown themselves to be the perfect adjunct to our continuous soil moisture measurements.
Visit Advanced Viticulture at Unified Wine and Grape Symposium booth 1245.
We are a full-service vineyard management and viticultural services company. Managing high-end vineyards in the north coast and providing technical services throughout the California coast and beyond. Our technical specializations are irrigation, soils evaluations and vineyard development planning, vine nutrition, sensing and automation technologies.
We have active partnerships with numerous sensor and telemetry companies, including Aquacheck soil moisture probes, Davis Enviromonitor system, Lumo automatic valves, Li-COR real ET sensors, Florapulse in-plant microtensiometers, Well Bubbler monitoring systems, and many others.
We have a new information portal (designed by us!) that integrates data flows from numerous data systems, so we can put all of your information in one set of dashboards for better decision making. If you want to make better use of your water and weather related information, let us connect you up. No additional hardware needed!
An interview with Christian Klier of Turrentine Brokerage - These are lean times. Or at least, they sure seem that way for many a grapegrower. As a viticulturist, market analysis is out of my wheelhouse. I wanted to sit down with someone who could give me a better idea about where the market is actually headed.
A diamond is forever, just like this bad market isn't | Advanced Viticulture
These are lean times. Or at least, they sure seem that way for many a grapegrower. As a viticulturist, market analysis is out of my wheelhouse. I wanted to
What Does a Prolonged Heat Wave Mean for the Vintage?
We are wrapping up a particularly hot July. The last time I had to write about heat stress was 2022, so this year seems to be making up for 2023’s persistent coolness. We all remember 2022. We had a couple hot days in late June that did quite a bit of damage in some vineyards. Then in late August, the sun parked itself right on top of California for three weeks, frying everyone’s hope of a decent harvest.
This year, the heat has come earlier and hasn’t quit. One measure Mark Greenspan and I like to look at is amount of time temperatures exceed 100°F and 105°F thresholds. Anything over 100 usually slows down vine growth and metabolism. Anything over 105 causes serious damage.
Here’s a comparison of 2022 and 2024 so far in the Russian River Valley.
And here’s Calistoga…
At least in Calistoga, 2024 is just a shifted version of 2022.
Now, these are ambient air temperatures. Fruit exposed to full sun can be as much as 15°C (27°F) over ambient temperature, which we initially found hard to believe, but there are numerous studies indicating this. Many of you got there this month. Some growers have experienced complete crop loss due to sunburn and shrivel. Tissue temperatures above 50°C (122°F) causes oxidative stress and cell death leading to the telltale signs of sunburn. This kind of extreme heat can also denature the proteins responsible for fruit maturation. This fruit may look alright immediately following the heat event, but it will never catch up in terms of color or maturity. We’ve all seen those pink berries that never really fully color up. The good news, if there is any, is that this fruit can be easily eliminated in late-season thinning passes as it looks very different from unburned fruit. I recommend leaving it as a physical barrier that can protect your remaining fruit until the survivors are fully through veraison.
But what about this remaining fruit…if you have any. Unexposed, shaded fruit is usually on par with ambient temperature. Ambient temperature is still really hot. What does an early and prolonged heat wave mean for the surviving vintage?
Read the rest of the article here.
Putting together budgets for next year?
How about investing in soil moisture and weather monitoring?
Soil moisture probes allow you to see how much water you have in the soil and how deeply each irrigation goes. If you want to water less or water more efficiently, probes can help you do that.
How hot did it get at that mountain vineyard everyone forgets about? How are growing degree days stacking up with respect to your valley floor vines? Get yourself a weather station and have all your vineyard weather data available at a glance. Get frost alerts or heat notifications when it's time to call the crews in.
email loni@advancedvit.com for more information.
I Got Frosted…Now What?
I had an macroeconomics professor preface the start of the semester stating that any question asked in his class was answerable with “it depends”…or “China”. While I don’t remember a ton about that class or the intricacies of U.S. tariff policy towards Chinese manufacturing, I find that at least the former part of that statement applies to frost season.
In this case, how you handle your frost damage depends on a few factors. How hard did you get hit? When did the damage occur? What are your winemaking goals? Let’s start with this last one.
What wine is this going into?
Frost damage always looks like Armageddon the morning after. Give it a month though, and it may look not much different than normal. You may even get just as big a crop as you would have if no frost had occurred. This is because the vine is resilient and pushes a lot of secondary and tertiary buds to make up for your burned-up primary bud.
Whatever fruit you have from these later shoots is going to develop later than your original fruit on surviving canes. In terms of sugar, the grapes will most likely catch up (at least here in California) since sugar accumulation reaches a plateau around 24 brix, more or less and then the berry hangs in there without additional sugar. After that any gains in brix are due to dehydration rather than grape metabolism. If sugar and yield are your principal concern, a mild frost event isn’t as big a deal as your overactive mind is making it.
There’s a lot more to wine quality than just sugar of course. Phenolic and aromatic maturity are untethered from sugar accumulation. In the case of a frost damaged block where half the fruit-supporting shoots emerged two weeks later than the other half, this discrepancy will be noticeable. You can’t very well tell a crew to pick only ripe fruit in the middle of the night, so if you’re a high-end winemaker who meticulously chooses a picking date based on all the data, you’re better off dropping the fruit from either the secondary growth or the primary growth. This will at least leave the block uniform.
Timing is important when it comes to fruit thinning a frost-damaged block. Whichever round of growth you intend to keep, you'll want to thin when crews can clearly distinguish between the fruit on surviving canes and those that emerged after the frost.
Catch a tiger by the toe
Do I choose the survivors or the second wave of growth? As a physiology refresh, a dormant grapevine bud is a compound bud composed of a large primary and a secondary and often a tertiary bud. The primary is usually the first that pops off and in the case of a frost event, is the one that gets smoked. This bud is usually the most fruitful, but by no means the “best”. The fruit produced from secondary and tertiary bud may be smaller but will end up giving you high-quality wine just the same. In fact, given that these buds essentially break bud a couple weeks later may be beneficial if you want a later harvest date or even better weather during fruit set.
In this case, what you get rid of depends on preserving yield. Some varieties and clones have limited or no fertility on their non-primary shoots. A few weeks after the second round of growth breaks bud, you should see how many inflorescences the new canopy will give you. This will give you a preliminary idea of which generation you want to keep.
In this picture, the damaged shoot has pushed a lateral. In this case it's best to remove the damaged shoot and let the bud at the base of the shoot grow instead. This will produce better crop and better wood. The time to actually eliminate unwanted fruit is green-drop (beginning of veraison). If you want to keep your primary crop, drop the green fruit. If you want to go with your later (secondary) crop, drop the pink clusters. If you eliminate fruit before the green drop stage, you’re likely to have bigger berries than if you had waited. That said, dropping fruit during lag phase won’t create bigger berries, but at that stage, the two sets of fruit are difficult to tell apart. Late in the season, approaching veraison, the berry has reached its final size and the risk of big berries has passed. Dropping fruit any later than green drop stage however, and you risk not being able to identify second growth fruit from primary growth fruit.
Beware recovering laterals! Frost doesn’t always burn up the whole shoot. Often the shoot tip gets fried since it is the most susceptible tissue. This leaves the primary shoot without its apical meristem and as a result, the surviving shoot pushes its lateral buds and grows from there. While grapes from the secondary and tertiary bud are fine and may be just as plentiful as that coming from the primary, you don’t want fruit from any lateral buds. This fruit will usually be much later and of lower quality.
A truncated primary shoot that is sending off laterals will prevent the secondary buds from pushing. In these cases, it is best to eliminate the damaged primary shoot as soon as possible and wait for another bud on the position to push. This is especially important if your vines are spur-pruned and you intend to use that shoot as a spur next year. The damaged primary will be permanently girdled and will never recover enough to give healthy shoots in the future.
Read the rest of the article here.
Look who's talking...
Mark your calendar for the Vineyard Irrigation Master Class organized by the Sonoma County Vit Tech Group. Advanced Viticulture is a proud sponsor and AV's own Mark Greenspan and Loni Lyttle are both speaking at the event.
Where: SRJC Shone Farm
When: June 6, 2024 10am-3pm
See the schedule below. Click here to register.
But before that, check us out on May 8th at David Bruce Winery in Los Gatos. Mark Greenspan and Loni Lyttle are excited to be presenting on floor management and till verses no-till.
Contact loni@advancedvit.com for more information.
Are the New Groundwater Management Plans Being Watered Down by Weak Monitoring Methods?
"GROUNDWATER . You can't see it, but millions of Californians depend upon it as a vital source of water for their homes and businesses." Those are not my words but the introductory words for the promotional video that appears on the SGMA (Sustainable Groundwater Management Act) website1 . The statement is a rather simply worded way to convey the obvious: that groundwater is vital to our livelihood here in California, and especially important to honoring and sustaining our agricultural heritage. While groundwater provides needed sustenance for numerous rural, as well as urban communities, it is agriculture that demands the lion's share of the resource.
Central Valley agriculture turns to groundwater pumping whenever drought or poor rainfall years reduce the availability of surface water deliveries. Cries for construction of more reservoirs to capture and store more stormwater and snowmelt so that canals can be filled with more water are always being heard. Yet, apart from the Smith River, all river systems in California are currently dammed2 . The current reservoir storage capacity in California is approximately 50 million acre-feet. Compare this to 850 million acre-feet, which is the estimated groundwater storage capacity in California. According to my calculations, groundwater resources are 17 times more plentiful than surface water resources.
Indeed, groundwater is a wonderful resource for California; and because it is so plentiful, it has been pumped mostly without regard to its sustainability. It helps that "you can't see it" because, in that way, it may seem to be an unlimited resource. But it isn't. Many large water basins are over-drafted, meaning that more water is pumped from them than is being replaced by natural means. In some cases, such as parts of the Central Valley, the overdraft has caused land subsidence.
Groundwater pumping in the Central Valley began in the 1920s, and land subsidence of over 25 feet was measured in some locations as far back as 19703 . That's truly scary, not only because the land and everything on it dropped about as much as a first down in football over that 50-year period, but because the aquifer also got squashed by that much. And now, 50 years later, how much more has it sunk? With subsidence, no means of restoration can restore that groundwater capacity. It's lost forever.
Not all groundwater basins cause that kind of land subsidence as they are over-drafted. For instance, the Paso Robles groundwater basin, which is currently critically over-drafted, remains intact and can hopefully be replenished by natural (or augmented natural) means if the overdraft situation can be reversed.
Subsidence, i.e. sinking land, can damage water-moving infrastructure that relies on gravity.
SGMA to the Rescue
The Sustainable Groundwater Management Act was enacted in 2014. Medium-priority and high-priority water basins were identified throughout the state, as well as critically over-drafted basins at one extreme and low-priority basins at the other extreme. The critically over-drafted basins, as well as those ranked medium- and high-priority, were assigned over 250 different management zones which were/are to be over-seen by individual Groundwater Ser vice Agencies (GS As). Each GSA has been tasked to develop a Groundwater Sustainability Plan (GSP) to be approved under SGMA by the California Department of Water Resources (DWR ). By 2020, GSPs were submitted for the critically over-drafted basins and, by 2022, for the medium- and high-priority basins.
GSPs must consider six sustainability indicators: Declining groundwater levels, surface water depletion (from shallow groundwater zones), degraded water quality, reduction in water storage capacity, land subsidence and seawater intrusion. If plans are accepted, then the local GSA implements the GSP; otherwise, the basin is turned over to the State Water Board as a backstop, which nobody wants because the water board regulations will be overly generic and heavy-handed with management compared to that of a local GSA that knows its specific situation better than a state-wide agency and is better able to connect with its constituents.
The beauty of SGMA is that it provides for local management of groundwater resources, with oversight by the DWR . The DWR also claims to provide some funding for projects to implement the GSPs, but from what I've heard (and it's not comprehensive), that funding may not be that easy to obtain. The DWR requires annual reports from the GSAs and implements five-year evaluations of each GSP to determine progress. GSAs have the authority to impose local fees.
Monitoring groundwater levels is not terribly difficult. Groundwater levels can be monitored in existing wells, or specific monitoring wells can be installed at key locations within each basin. Drilling monitoring wells isn't cheap, though. Water depth can be measured by hand with several techniques, including pumping air into a plastic tube whose outlet has sunk to a known depth in the well column. The pressure required to clear the tube is equal to the water pressure of the column of water above the outlet. Well companies often install these "sounding tubes" in the wells and use hand pumps to measure water levels. Similarly, this process can be automated for continuous monitoring. A San Luis Obispo-based company produces "The Well Bubbler," which automates this process. Similarly, a pressure transducer can be dropped down a well to a known depth to measure the water column. My company has set up many wells in the North and Central Coasts for continuous monitoring, primarily using The Well Bubbler system. The DWR can supply funds for some of these efforts to monitor groundwater levels.
The Well Bubbler offers a non-invasive way to measure well depth. From this real-time data you can infer speed of recharge and monitor overdrafting, which can damage your well pump.
Monitoring Grower Water Use
This is where it gets dicey and a bit controversial in my opinion, if not downright infuriating. Unlike SB88, which requires the use of flowmeters by water users to measure water diversions, SGMA is fuzzier and more generic about how GSAs may monitor water users' pumping volumes.
I was sitting in on a local GSA meeting a few months ago as I had the opportunity to do a few times in 2023. The meetings are public, and at least this particular one is typically available on-line during the meeting. I'm not going to mention the actual GSA because I respect all the board members and think they are doing a fantastic job and genuinely have sustainability in their hearts and minds; however, I was dumbfounded to learn that remotely sensed evapotranspiration (ET ) methods were going to be used to quantify groundwater pumping volumes per property within the GSA's purview.
I had been previously under the impression that growers (and residences) would be required to monitor their pumping volumes with flowmeters, much like under SB88. I had heard grumblings about the inaccuracy of flowmeters, their maintenance and grower resistance to their use and reporting requirements. In truth, if a flowmeter is installed according to spec, it will be accurate. And while mechanical flowmeters do wear out over time, the more current electromagnetic meters have no moving parts and, therefore, require minimal maintenance. On the other hand, I can't argue against the fear that growers will be resistant to flowmeters on their wells, and things could get ugly for a while if growers are required to report their actual pumping volumes. Indeed, the GSA does have the authority to impose such a requirement, unpopular as it would be.
Remotely Sensed ET
Two sources of ET data are being considered to estimate consumption: OpenET and Land IQ. OpenET is a resource that according to its website4 , is led by NASA, the Desert Research Institute (DRI) and the Environmental Defense Fund (EDF ), with in-kind support from Google Earth Engine. The OpenET model is available at no cost to the user and currently covers the 17 westernmost U.S. states, with plans to expand its coverage further. Land IQ5 is a private company, based in Sacramento, that provides many different ser vices in the environmental realm, but their Land IQ ET product is the ser vice that appears to be most readily adopted by GSAs. Land IQ focuses on California, namely 3.3 million acres in the Central Valley, but is expanding with GSA demand to other parts of the state.
Both services have data sets that can be measured for specific locations on a grid or field, but Land IQ can aggregate its data over districts and regions, hence its attraction to local GSAs. OpenET's spatial resolution is 30m2 (0.22 acres) whereas Land IQ's resolution is a much sharper 10m2 (0.02 acres). Both OpenET and Land IQ use ground-based, gridded weather data sets that include parameters, such as solar radiation, air temperature and humidity, wind speed and precipitation. Both ser vices also use satellite data to provide surface temperature and surface reflectance information. Both use Landsat, which provides updated imager y ever y 16 days, as well as Sentinel, which provides imager y ever y five days. Other satellites are also used. Note that clouds and smoke will interfere with the measurements, so those images are excluded.
OpenET employs six different ET models by using the ava ilable data; and while each of the model results may be obtained from the system, most commonly, an ensemble average is used, with automatic removal of any outliers. Three of the models generated by OpenET use remotely sensed shortwave reflectance and thermal imager y, another uses remotely sensed surface reflectance and crop-type information, and two others are further simplified models. Land IQ is less transparent about the models it uses but takes ground-based measurements of actual ET using eddy covariance (most accurate), as well as surface renewal/energy budget methods (less accurate than eddy covariance) to calibrate its model on a consistent basis.
It appears that most GSAs are moving toward the Land IQ service, which to me seems like it may have both an accuracy and a precision edge over OpenET, if only because it is focusing on California and is continuously calibrating itself.
But it is still only a measurement of consumptive use-not water application.
Flowmeters remain the only tried-and-true way to quantify water use.
Is ET Enough to Save Water?
My objection to using ET, as a surrogate to flowmeters, has been partially allayed by investigating these services. I reassured myself by looking at some output of OpenET and seeing that ET measurements do not fall to zero, during the winter, when vineyards (and most orchards) have no leaves on them. Indeed, there was ET occurring then, so the model can consider non-crop vegetation, as well as surface evaporation.
But does it truly capture a grower's water use? No, it does not!
ET measures consumptive water use, not applied water. Land IQ's brochure states this clearly. If a grower over-irrigates (i.e., applies more water than the consumptive use), the consumptive water use estimate doesn't change. Indeed, a grower could over-irrigate, causing runoff or deep percolation, and ET would remain unaffected. Does this matter? I think so. For one, it provides no incentive for a grower to irrigate more efficiently because their water use report will remain largely unaffected, regardless of what they do to conserve water.
What about frost sprinklers? They are a heavy user of water, and the ET model will report nearly nothing from them because there is very little vegetation present during spring frost season. Likewise, how about winter drip irrigation, a necessity for many growers in regions with little winter rainfall, especially during drought. Again, this water use is real but will not be captured by the remotely sensed ET model.
Where does the excessive water go? That is a little less clear. Some of it evaporates. The rest seeps into the ground below the root zone. The claim is that the deep percolation water just goes back into the groundwater. That may be the case in some but not definitely all cases as there is not always a solid hydrological connection between surface water and groundwater. Aquifers are commonly a few hundred feet below the surface (some are tens of feet and some many hundred feet below the surface). The vadose zone is the unsaturated zone between the surface and the capillar y fringe immediately above the aquifer. Excessive irrigation may eventually return to the aquifer, but it may just as likely run off into streams or just linger there for decades until the next big flood event.
So I contend that using ET alone is insufficient to encourage and reward more efficient irrigation of crops by growers and that without monitoring of actual use, we may find ourselves in the same predicament we are currently in. To measure actual water use, we need flowmeters ideally or at least pump power consumption records. It would be a shame if the only way we can reduce demand for a water basin is to take acres out of production because that's not the only solution. I know from firsthand experience that most growers could reduce their irrigation applications without productivity losses. I know that because I live in that world.
But the fact is that as the regulation is currently written, ET is an allowable method for consumptive use estimation. I had a brief email exchange with Timothy Parker, principal hydrogeologist for the DWR and co-author of the report "Hydrogeologic conceptual model in Paso Robles6 ," about my concerns regarding remotely sensed ET as a surrogate for water usage monitoring. He agreed with me about my concern and said that he had argued that very point with colleagues years ago during the development of SGMA . The adoption of ET over that of flowmeters was largely a political one, in his opinion, as requiring flowmeters would probably have meant SGMA's failure to be put into law. What a shame.
So for now, we must live with it and hope that our groundwater basins can be managed sustainably without knowing actual water draws. At least we'll be monitoring the aquifers more consistently and frequently than we had been in the preceding decades; so if we don't see progress, which I fear could be the case, GSPs will be eventually forced into metering actual flow.
The longer we let our groundwater basins decline, the longer it will take to bring them into sustainability. Realizing the actual effects on groundwater storage could take a decade or longer of groundwater level monitoring. And who knows how many years, after that, to enact the needed changes. It's time we growers take responsibility for our water use, demonstrate our water efficiency, improve our water efficiency and not simply talk about sustainability. Prove it-measure it!
Be sure to subscribe to Wine Business Monthly and check out the rest of the March Issue!
Also be sure to check out our latest blogpost on groundwater recharge.
What's in your soil?
Are you replanting a vineyard? Maybe you're trying to understand why your vines are struggling. Looking to improve quality, yield, or both?
Here at Advanced Viticulture we have the equipment and know-how to analyze and map your vineyard soil. You can then use this information to determine amendments and treatments as well as picking the best rootstock for your location.
Contact loni@advancedvit.com for more information.
Our EM sensor combined with boots-on-the-ground analysis creates colorful maps so you can best visualize how your soil changes. Apply only what you need where you need it.
Does a Lot of Rain Mean a Lot of Aquifer Replenishment?
I recently had the opportunity to sit down with Timothy Parker of Parker Groundwater Consulting in Sacramento, CA.
Loni Lyttle: So, I wanted to talk to you today about groundwater recharge. California, along with the rest of the western United States has been in a long drought and is facing serious issues with groundwater depletion not to mention subsidence, where the land is actually sinking due to overdrafting the aquifer. But then we get these two wet years in 2023 and 2024 (so far) with above average rainfall. I think this lulls people into a sense of security about California’s water situation and I’m not sure it’s that simple. I’m not a hydrogeologist so I wanted to get in touch with someone who knows more on the subject.
Tim Parker: You are right – the surface water reservoir drought is over but our groundwater reservoirs are still in drought conditions. So there’s a lot of recharge going on and we don’t always know how successful it is and whether or not it’s causing potentially adverse impacts. And I hate to start off on that point, but it is something we have to be concerned about.
There’s a lot of good information out there. Just in the last few years, the state has started putting a lot more information out on groundwater level information, including changes over a year that you can see visually.
One of the things in my research that I was surprised about was on subsidence in the Central Valley. We’re aware of the subsidence there. But when you look at the change in subsidence that’s being monitored on an annual basis, the change during those wetter years was much less. I thought that was pretty interesting because there is a significant lag time with subsidence. Once you have subsidence and you shut the pumping off, It doesn’t just stop altogether. It continues to subside for some period of time.
LL: That is interesting. I mean when I think of subsidence, I think immediately of the Central Valley just because I know it’s so severe. I mean the water that people are pumping there is ancient water, right? That basin filled up a long time ago?
TP: Yes and no. One of the things we found with the statewide aerial electromagnetic project is the way the sediments were deposited in the Central Valley, especially the San Joaquin Valley. So during the Pleistocene you had periodic glaciers, lots of ice and then melts. That action created these incised alluvial fans. (read more about this topic here.)
So that’s very coarse grain sediments coming off of the Sierra Nevada mountains. And actually Stanford’s done some work tracking subsidence data, groundwater levels, and precipitation. Through that you can see the water coming into the basin especially along those kind of superhighways for recharge coming off of the mountains. Now that’s fresh, young water coming in. But you’re right, most of the deeper water being pumped is old. Back in the 60s, there were some studies done and found that groundwater levels have dropped several hundred feet. And again, that’s where we are today. Groundwater levels have have continued dropping significantly, and that means you’re getting some recharge of fresher, younger water up on top, the pumping is mostly deeper, typically where the groundwater gets older.
Parts of the San Joaquin Valley has huge problems with depletion and associated subsidence. The economic impacts are big in these situations.
Subsidence, i.e. sinking land, can damage water-moving infrastructure that relies on gravity.
LL: So in the San Joaquin Valley for instance, how many years of water do they have left if they continue to pump as they have been?
TP: I haven’t looked into that. I do know it’s dropped several hundred feet over the decades. It’s about a 2 million acre-feet overdraft per year. That’s one of the estimates that’s out there. If pumping continues at the current rate, the basin has a limited lifetime, whether that’s a few decades or many decades.
The other issue in all of that is water quality. The deeper you go, you’re going to run into higher total dissolved solids in addition to the problem of land subsidence. Subsidence is a big economic driver because it affects infrastructure. The Central Valley and the state as a whole relies on moving water from where there’s more precipitation in the north to where there’s much less precipitation in the south. And these aqueducts and irrigation ditches, et cetera, are gravity drains. When the land sinks, that interrupts the flow, and so they’re having to do a lot of repairs. The other thing is that you have floods in different areas where you didn’t before. So that’s another risk and liability.
LL: So can you go more into where our groundwater comes from? How variable is groundwater within a given region or even within a given basin? I’ve seen it where we are. Even within Paso Robles, there’s so much variation. You have eastern Paso, which looks like an old western movie, but then the water is really good. There are good wells out there where you hit water at less than 100ft. Then growers in western Paso have to get their water out of fractured rock and it’s barely a trickle.
TP: It has to do with the geology and California has a very interesting geology. It was formed by tectonic plates pushing against one another. That formed the Central Valley as a structure. One plate underneath the ocean (oceanic plate) was subducted underneath the continental plate. That caused the subducted plate to melt and form the Sierra Nevadas. The Central Valley was what they call a forearc basin, where sediments were formed as part of an inland sea. And then marine sediments that were on top of the ocean plate were scraped up and formed into the coastal ranges. So you have these marine sandstone shales all folded up and deformed. And that’s the bedrock that you’re talking about in the Paso area on the west. And then the other thing that happened 20 to 30 million years ago, was that subduction zone changed to a transform fault, which you probably know the name of…the San Andreas fault. When that happened, there was this sort of northwest structural, tensional and extensional change that occurred.
As a result of the transition to San Andreas transform fault tectonics, you have all these northwest trending small basins in the coast ranges that are faulted as a result. And those filled with alluvium or sand, silt and gravel. And so those are the kind of the two types of basins you’re talking about. In the coast ranges, it’s typically more limited unconsolidated alluvial deposits, and fractured bedrock that doesn’t produce much water. It’s okay for a residence where you need five to ten gallons per minute. And then in the alluvial systems, you get a lot better production, typically. But anyway, that’s kind of the difference in that is whether you’ve got an alluvial aquifer or bedrock aquifer that you’re getting water from.
LL: These small coastal basins, is that what we have in northern California wine country. Are Sonoma and Napa in those little coastal basin areas?
TP: There’s so much diversity up there. I’ve actually worked in the Sonoma Valley for almost 20 years as a groundwater management consultant. Sonoma is one of the more complex basins because you have also volcanics and multiple faults there. What we like to say is that it’s “compartmentalized”. It’s got all these separate compartments. You can drill a well in the Sonoma Valley and move 25ft over and you might get water in one and nothing in the other. That’s how quickly things can change. It’s very complicated geology. The San Andreas is a fault zone that’s several miles wide. Then there’s a lot of other faults that are the same trend that run through these coastal basins. And then you have other faults that run to 90 degrees to that. So there’s all this different movement that’s occurring, and that’s what makes the hydrogeology complex. Some of those faults can be conduits and a lot of them can be barriers, so you can move from one side of a fault to another and get completely different geology and groundwater results.
This is a long one, but there's tons of great information! Read the rest of the article.
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Unboxing Owl Boxes
Did you know that owls are cannibalistic? Baby owls will feast on their owlet-siblings to reduce competition. Did you know that owls strike so fast they kill on contact? It’s the equivalent of getting hit with a truck…a truck with talons.
I love talking to bird people. They’re such sadists. Or rather, they look at the grim brutality of the natural world and dive right in. They’re the ones who root for the T-Rex in Jurassic Park. In Don’t Look Up, they’re most likely rooting for the asteroid.
So, when it comes to rodent control, a topic most people find icky, who better to consult than someone passionate about birds? Recently, I had the opportunity to sit down with John Schuster of Wild Wing Company in Sonoma County, Calif.
Schuster has had a fascinating career in forestry, firefighting and conservation. He also makes most of the owl boxes I see in the North Coast. It turns out if you ply him with a cappuccino, he’ll tell you all sorts of things about owls and how they benefit farmers.
Barn owls are not territorial so having multiple owl boxes per acre isn't overkill. I doubt they appreciate being woken up though...
What Is an Owl Box and What Is it Used for?
Owls are a cavity dwelling bird species. They eat a lot of nocturnal rodents, such as voles and pocket gophers. An adult owl requires on average 156 grams of food each night: that’s about the size of one gopher or two voles—double that if he’s got a mate back home. Baby owls require three to five times this per night, and a typical brood is between three to five owlets. If you have an owl box with a little owl family in it, you’re looking at 3 kilograms (about 6.5 pounds) of rodents per night.
The goal of your natural predation program should be this: establish a healthy population of breeders. Predators follow prey; so, if you have a high population of rodents, that should be enough to sustain many families of breeding owls. Owl families will consume many more gophers and voles than your bachelor birds. Owls won’t even mate unless there’s enough food on the table to support offspring. I know many farmers who have more than enough gopher meat to go around.
It’s always important to remember that the vineyard is far from a natural place. Under untouched conditions, owls would be able to find homes in tree hollows and the like. That kind of real estate isn’t as available among acres and acres of vines and trellis hardware. If your rodent population has blown up, it’s probably linked to habitat loss of native predators. Owl boxes allow for the reestablishment of what’s been lost. For some of you, that is reason enough to put some of these in. However, not all owl boxes are created equal.
A Wild Wing technician surprised this ghosty girl while cleaning out the owl box. Having a trap door makes this activity much easier.
Owl City: Location and Density
Owls will hunt within about a mile and a half radius from their home. Barn owls and Screech owls are not territorial, so there’s no problem having considerable overlap in hunting grounds. John says it’s best to have an owl box every 100 to 200 yards if the rodent population is moderate, with owl boxes every 60 yards if you want to take a more aggressive approach. That seems like a lot to me; but if you are planning on relying exclusively on owl boxes for gopher and vole control, you will want to build a healthy population.
On the road again...to Unified 2024
Are you going to the Unified Symposium? Come check us out at Booth 2038! We've got a lot of cool stuff we'll be rolling out this year and we can't wait to tell you all about it!
Contact loni@advancedvit.com if you need a ticket to the trade show.
About
Advanced Viticulture's principal viticulturist is Mark Greenspan, Ph.D.
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| Title | Name | Phone | Extension | |
|---|---|---|---|---|
| Dr. | Mark Greenspan | mark@advancedvit.com | 707-838-3805 |
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| Locations | Address | State | Country | Zip Code |
|---|---|---|---|---|
| Advanced Viticulture, Inc. | 930 Shiloh Road, Bldg. 44, Suite E, Windsor | CA | United States of America | 95492 |
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